X-ray tubes may be used in a variety of applications to scan objects and reconstruct one or more images of the object. For example, in computed tomography (CT) imaging systems an X-ray source emits a fan-shaped beam or a cone-shaped beam toward a subject or an object, such as a patient or a piece of luggage. The terms “subject” and “object” may be used to include anything that is capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the X-ray beam by the subject. Each detector element of a detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis. The data processing system processes the electrical signals to facilitate generation of an image.
Generally speaking, in CT systems, the X-ray source and the detector array are rotated about a gantry within an imaging plane and around the subject. Furthermore, the X-ray source generally includes an X-ray tube, which emits the X-ray beam at a focal point. Also, the X-ray detector or detector array in some systems includes a collimator for collimating X-ray beams received at the detector, a scintillator disposed adjacent to the collimator for converting X-rays to light energy, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. In other systems, a direct conversion material, such as a semiconductor (e.g., Cadmium Zinc Telluride (CdZnTe)) may be used.
The X-ray tube, for example, may include an emitter from which an electron beam is emitted toward a target. The emitter may be configured as a cathode and the target as an anode, with the target at a substantially higher voltage than the emitter. Electrons from the emitter may be formed into a beam and directed or focused by electrodes and/or magnets. In response to the electron beam impinging the target, the target emits X-rays.
The size of the electron beam may affect resolution. For example, a smaller diameter electron beam may allow generation of higher resolution focal spots. Certain known X-ray tubes have drawbacks regarding electron beam sizing. For instance, conventional X-ray tubes may produce electron beams that have a generally large diameter that inhibits high resolution focal spots. Further, differently configured resolutions of focal spots may be desirable in connection with different applications or uses of X-ray scanning. However, conventional X-ray devices may be limited to a single diameter of electron beam, and thus, a single resolution of focal spots, thereby limiting the usefulness of a given device for different applications or procedures.